Thunderstorms began to develop along a weak frontal boundary across southern Minnesota, between Springfield and Mankato. These storms moved to the east across portions of south central and east central Minnesota and spanned numerous reports of large hail, very heavy rainfall, and gusty winds. Most of the hail stones were one inch in diameter, however, a few reports of up to tennis ball size was reported near Mankato. These storms moved into west central Wisconsin and caused more hail near Lake Pepin. Another complex of storms moved across northeast South Dakota, and into west central Minnesota during the late evening. These storms caused more large hail reports during the early morning in east central Minnesota.